Takes a bunch of portable pixmap as input. Chooses ncolors colors to best represent all of the images, maps the existing colors to the new ones, and overwrites the input files with the new quantized versions.
If you don't want to overwrite your input files, use the -ext option. The output files are then named the same as the input files, plus a period and the extension text you specify.
Verbose explanation: Let's say you've got a dozen pixmaps that you want to display on the screen all at the same time. Your screen can only display 256 different colors, but the pixmaps have a total of a thousand or so different colors. For a single pixmap you solve this problem with ppmquant; this script solves it for multiple pixmaps. All it does is concatenate them together into one big pixmap, run ppmquant on that, and then split it up into little pixmaps again.